1. Field of the Invention
This invention relates to a pipe joint construction. More particularly, this invention relates to a pipe joint construction for use in a coolant pipe laid in an air conditioner on an automobile, for example.
2. Description of Prior Art
As is widely known, the air conditioner on the automobile, for example, is provided with a coolant pipe forming a cooling cycle system and a hot water pipe forming a warming cycle system and is operated to cool or warm the space in the automobile by leading a coolant or a hot water such as engine cooling water to a heat exchanger, there to absorb or radiate heat and cool or heat the air.
To complete the cooling cycle system and the warming cycle system as prescribed by using pipes, all the adjoining pipes are joined with joints. Various joint constructions have been proposed for the union of such pipes. In the joint construction illustrated in FIG. 1 and FIG. 2, for example, a pipe joint 1 comprises a nut 3 adapted to collide against the rear side surface 2a of a bead 2 formed at the leading end of a first pipe P.sub.1 and a union screw 7 having an inner end surface 6 thereof adapted to collide against a radially expanded portion 5 formed at the leading end of a second pipe P.sub.2 for embracing therein an O-ring 4 fitted on the terminal side base of the aforementioned bead 2, so that the pipe joint 1 will connect the first pipe P.sub.1 and the second pipe P.sub.2 while sealing the adjoining pipe ends by compressing the O-ring 4 between the circumferentially opposed pipe surfaces.
This joint construction, however, has the possibility that the aforementioned bead 2 will sustain damage when the nut 3 is tightened excessively against the union screw 7 or when the tightening is repeated time and again. In the union or disunion of any pipe joint of this kind, two wrenches of exclusive specifications are used, one for keeping the union screw 7 in a fixed state and the other for rotating the nut 3 until the pipe ends are joined. During the tightening work of this nature, the torque generated cannot be easily controlled. If this tightening is given to any excess, the leading end 8 of the inner end surface 6 of the union screw may deform the end part 5a of the radially expanded portion 5 of the second pipe P.sub.2 possibly to flatten the end part 5a and push the surplus of the wall thickness upwardly in the position as illustrated. Once this deformation occurs, an attempt to move the nut 3 toward the right in the illustrated position for disunion of the pipe joint 1 may end up in failure because the apex of the end part 5a of the aforementioned radially expanded portion 5 rises to a height of h above the level of the leading end 9 of the female thread of this nut 3. A decrease of the height of the end part 5a of the radially expanded portion 5 may appear to be an effective solution for this disadvantage. The work of decreasing this height, however, is very difficult because of dimensional tolerance of working.
Further, the radially expanded portion 5 is never allowed to deform inwardly because the distance l between the inner end surface of this radially expanded portion 5 and the outer wall surface 10a of the leading end 10 of the first pipe P.sub.1 is rigidly controlled to warrant a contraction of the O-ring 4 (normally about 25% of the diameter of the O-ring). In this respect, the tightening work of the aforementioned nut 3 and union screw 7 calls for great care. Particularly in a narrow space such as in the engine room, this work entails unusual difficulty.
Japanese Utility Model Laid-Open No. SHO 55(1980)-29,750 discloses a metal pipe joint construction characterized in that a half union screw and a flared nut on the pipe joint are so designed that their opposed end walls will come into intimate mutual contact when one of the metal pipes to be joined has its end portion tapered outwardly toward the end and the other metal pipe has a substantially perpendicularly extended flange portion formed in the portion approximating the end thereof and a tubular portion suitable for insertion into the opposite metal pipe formed in the further leading portion thereof, a resilient sealing material is inserted in the annular space of a triangular cross section defined by the aforementioned tapered end and the flange portion and the tubular portion and, with the half union screw and the flared nut fitted around the two metal pipes, the aforementioned tapered end is brought into contact with the flange portion and further pressed thereagainst so as to be slightly deformed. This joint construction is substantially equal to the joint construction of FIG. 1 and FIG. 2, except that the metal pipe provided with the tapered end possesses no radially expanded portion in the part approximating the end thereof. Thus, it has the same problem.
An object of this invention, therefore, is to provide a novel pipe joint construction.
Another object of this invention is to provide a pipe joint construction which, despite the tightening work performed by the same procedure as followed heretofore, never encounters the situation that the nut will become inseparable.